1. Field
The present specification generally relates to molds and, more specifically, to molds for shaping glass.
2. Technical Background
The current demand in modern electronics devices for thin, three dimensional glass substrates that have very high levels of surface quality has produced a need to find new materials and processes that are commercially capable of providing defect-free shaped glass substrates. Shaped glass forming generally refers to high temperature processes that involve heating the glass to be formed to a temperature at which it can be manipulated, and then conforming it to a mold to get the designed shape. Classic methods of shaping glass substrates include television tube forming, where a softened glass gob is pressed between male & female molds, and bottle forming, where glass is blown in a pair of hollowed molds.
In shaping operations, mold material selection is often the key to success. In order to optimize the shape and surface quality of the formed glass article, the mold material must: 1) have excellent oxidation and corrosion resistances at the process temperatures; 2) have minimal reaction with the glass (no sticking); and 3) be strong enough at the process temperature in order to resist the deformation and distortion from the forming force.
In reality, it can be difficult to select one material to meet all the above requirements. One solution has been to apply coatings on the mold surface to get the combined merits of the various materials to achieve forming success. Coated molds are the most commonly used in the glass forming industries today. Uncoated molds (or bare molds) are rare, and are limited to lower-end glass products such as bottles and certain glassware that don't require high surface quality. If bare molds are used, there is generally some level of lubrication applied to help with the forming process and to retain surface quality. These lubricants are difficult to consistently apply and require a secondary cleaning step to remove. For higher-end products, especially for optical-quality products such as press-formed camera lenses, coatings have been deemed as essential.
Although coatings help to meet the challenges in glass forming process, they create new problems. For example, coatings can add significant costs and new variables to manage the processes. More importantly, coatings often deteriorate during operation and lose functionality, limiting the lifetime of the mold and necessitating frequent re-coating. Therefore, there is an unmet need in the area of high-end, high quality glass substrates to obtain better mold materials that are commercially capable of providing defect-free, shaped glass substrates.